The invention relates to multi-color displays and, in particular, to multi-color displays based upon light-emissive devices incorporating semiconductor phosphor materials.
Flat panel displays offer various advantages over conventional displays, such as a greatly reduced physical profile, lower power and voltage requirements, a reduced heat output, and lighter weight. Flat panel displays consist of an array of light-emissive devices integrated on a single substrate. To form an image, individual light-emissive devices radiate light when lit and are nominally dark when in an unlit state. Flat panel displays have extensive commercial applications and can be used in any product which requires light emission, from simple panel lights to complex displays in industrial fields including automotive instrumentation, consumer televisions, consumer electronics, consumer lighting, aerospace applications, and military uses. Devices used in such flat panel displays may also be suitable for use as lasers in fiber optic communications.
Flat panel displays capable of full multi-color display, usually consisting of three displayed colors such as red, green, and blue, are structurally challenging to fabricate on a single substrate. There are two types of integration models for fabricating light-emissive devices to form multi-color flat panel displays: vertical integration in which the various phosphor films for the light-emissive devices are layered vertically to form a stack, and lateral integration in which the devices are arranged side by side. Vertically-integrated devices are more compact and have a smaller footprint on the substrate surface than laterally-integrated devices. However, the electrical interconnection and operation of vertically-integrated light-emissive devices presents serious practical difficulties. In laterally integrated structures, each phosphor film can be grown at optimized conditions for the emission of each color. By changing the emission intensity from individual light-emissive devices, a multi-color flat panel display may be realized without the electrical interconnect problems of vertically integrated light-emissive devices.
Among the most promising phosphor materials for achieving a multi-color color display is gallium nitride doped with various rare-earth impurities. Gallium nitride thin films are not very robust chemically and, therefore, wet etching with chemical solutions cannot be used to form interleaved arrays of light-emissive devices. Although it is possible to use plasma-based techniques to dry etch rare-earth doped gallium nitride thin films to form active elements for various different colors, the etched surfaces are roughened by the etching process. As a result, it is difficult to grow high quality rare-earth doped gallium nitride thin films for the light-emissive devices emitting the other two colors once the rare-earth doped gallium nitride thin film for the light-emissive devices emitting the first color is formed. Therefore, despite the promise of rare-earth doped gallium nitride as a phosphor material, multi-color displays based on such phosphor materials have yet to be successfully fabricated.
Therefore, there is a need for a multi-color flat panel display having laterally-integrated light-emissive devices capable of emitting light of at least three different wavelengths or colors, and a method of fabricating such multi-color flat panel displays.
The invention is related to the lateral integration on a single substrate of light-emissive devices emitting light, typically by electroluminescence, with at least two different wavelengths and, in most applications, emitting light with three different wavelengths, such as the three primary colors (red, green and blue) of the visible portion of the electromagnetic spectrum, at an intensity sufficient to be observed visually under various conditions, including daylight ambient lighting. The invention is premised upon a lift-off technique that relies upon a sacrificial layer of a material such as spin-on-glass. According to the invention, a multi-color flat panel display is provided that includes a substrate, a plurality of transparent electrodes, and a plurality of first, second and third light-emissive active elements each disposed between said substrate and a corresponding one of said transparent electrodes. The first, second and third light-emissive active elements are arranged such that each of said first light-emissive active elements is laterally adjacent on said substrate to one of said second light-emissive active elements and one of said third light-emissive active elements. The first, second and third light-emissive active elements emit light of at least one differing wavelength resulting in different colors from within the visible portion of the electromagnetic spectrum.
According to the invention, a method is provided for fabricating a multi-color flat panel display that includes forming a first sacrificial layer on a substrate, providing a plurality of first openings in the first sacrificial layer to the substrate, depositing a first semiconductor phosphor material on the substrate to cover the first sacrificial layer and the substrate through the plurality of first openings, and removing the first sacrificial layer and the first semiconductor phosphor material covering the first sacrificial layer to leave a plurality of first active elements of the first semiconductor phosphor material on the substrate at positions corresponding to the plurality of first openings. The method further includes forming a second sacrificial layer on the substrate and the plurality of first active elements, providing a plurality of second openings in the second sacrificial layer to the substrate in which each of the plurality of second openings is adjacent to a corresponding one of the plurality of first active elements, depositing a second semiconductor phosphor material on the substrate to cover the second sacrificial layer and the substrate through the plurality of second openings, and removing the second sacrificial layer and the second semiconductor phosphor material covering the second sacrificial layer to leave a plurality of second active elements of the second semiconductor phosphor material on the substrate at positions corresponding to the plurality of second openings. Transparent electrodes are then deposited on the plurality of first active elements and the plurality of second active elements to complete the fabrication of the light-emissive devices forming the multi-color flat panel display.
In an alternative embodiment of the method of the invention, the method of fabricating the multi-color flat panel display may further include forming a third sacrificial layer on the substrate, the plurality of first active elements, and the plurality of second active elements, providing a plurality of third openings in the third sacrificial layer to the substrate in which each of the plurality of third openings is adjacent to corresponding ones of the plurality of first active elements and the plurality of second active elements, depositing a third semiconductor phosphor material on the substrate to cover the third sacrificial layer and the substrate through the plurality of third openings, removing the third sacrificial layer and the third semiconductor phosphor material covering the third sacrificial layer to leave a plurality of third active elements of the third semiconductor phosphor material on the substrate at positions corresponding to the plurality of third openings, and depositing transparent electrodes on the plurality of third active elements.
The objects and advantages of the invention will be further appreciated in light of the following detailed description and drawings in which: